The disclosed invention involves a percutaneously placed artificial valve to maintain bodily fluid flow in a single direction. It opens and closes with pressure and/or flow changes. The invention may be placed anywhere flow control is desired. To facilitate the discussion of the disclosure, use as a heart valve will be addressed. Heart valves are selected because they provide the highest risk to the patient during placement, and in terms of lowering the risk while providing a superior device the advantages of this valve are clearly presented. It is understood that the device and method disclosed are available to all valvular needs.
Cardiac valve prostheses are well known in the treatment of heart disease. The normal method of implantation requires major surgery during which the patient is placed on a heart-lung machine and the patient's heart is stopped. Once the surgery is complete, the patient can expect an extended hospital stay and several more weeks of recuperation. A mortality rate of five percent (5%) is common. For some patients, surgery is not an option because age or some other physical problem prevents them from being able candidates for surgery due to the inherent dangers and the likelihood of death therefrom.
The valve devices themselves fall into two categories, either biological or mechanical. Biological heart valves are either homograft (a recent human harvest), allograft (a stored human harvest) or xenograft (a stored animal harvest). Homografts are rare because of the well known problems of locating and matching human donors in both tissue type and size. Allografts are also in short supply because of lack of donors. Xenografts are common and well accepted, usually from bovine or porcine donors, and many times the actual heart valve from the animal is used. These devices may be accompanied by immunological rejection from the human body when sutured directly to human tissue and require the patient to take anti-rejection drugs which suppress the immune system. Generally, the valves are treated to reduce the antigenicity of the valve tissue, but the effect is to limit the life of the valve to about ten years.
Mechanical valves may be either a ball valve or a leaflet valve having one to three leaflets. One leaflet valve, U.S. Pat. No. 5,469,868, closely resembles a biological valve having three synthetic resin leaflets. Mechanical valves are susceptible to clot formation and require the patient to maintain a strict regiment of anticoagulant drugs which carry their own associated risks. Furthermore, some mechanical valves are prone to wear leading to failure, and some materials for mechanical valves are subject to supply problems.
The majority of these artificial valves require surgery and the stopping of the heart as discussed above. During implantation, the valve must be sewn in place either at the natural valve location or at a location adjacent to the natural valve. Even new laproscopic techniques, while substantially less invasive, require general anesthesia and a heart-lung machine. There are artificial valves which claim to have overcome the problems of implantation of the commonly used valves.
Three artificial valves which claim the ability to be placed percutaneously comprise the nearest prior art. They are the Tietelbaum valve, U.S. Pat. No. 5,332,402; the Pavcnik valve, U.S. Pat. No. 5,397,351; and the Andersen valve, U.S. Pat. No. 5,411,552. Each of these devices allow placement by minimally invasive techniques. However, each of the devices have disadvantages upon which the disclosed invention greatly improves.
The Teitelbaum valve uses nitenol to form each of the two major elements of the valve. It is a mechanical valve, and as such is prone to embolism formation. The two types of stoppers, a ball and seat and an umbrella and seat, each reduce the passageway diameter through the valve thereby reducing the efficiency of blood flow through the valve, and the efficiency of the cardiovascular system itself. Being of two separate components, the movement adds extra complexity leading to wear and improper seating. The abundance of metal in direct contact with the tissue requires a hydrophilic coating which may or may not prevent stenosis in the valve passageway. This valve may only be placed in the natural valve's position and not elsewhere in the vascular system. Also, the nitenol design proposed requires cooling to make it sufficiently compliant to fit within the placement catheter. Cooled nitenol does not exhibit sufficient force upon warming and reformation of its intended shape to maintain a seal between the stent and the tissue. Lastly, both elements must be inserted independently of the other requiring multiple delivery catheters.
The Pavcnik valve is also a mechanical valve of ball and seat design. It utilizes a Gienturco stent (U.S. Pat. No. 4,580,586) capped by a cage to comprise a complex restraining element for the ball which is difficult to manufacture. The restraining element must be attached to the seat by a connecting member to maintain the proper distance between the two. The ball is made of latex which can cause a reaction with living tissue. The seat is comprised of two rings, one smaller than the other, displaced from each other by nylon mesh. Both the seat and the restraining element are stainless steel which must be fairly stiff and non-compliant to maintain sufficient outward bias thereby severely restricting the natural movement of the cardiovascular system at the point of implantation. There are multiple joints which must be soldered together increasing the potential for joint failure and breakage. This device requires hooks to maintain patency in the tissue, requiring surgery to remove once deployed. Repositioning is not possible because of the hooks. The balloon must be inserted in a deflated state and filled after placement within the cage and seat. The filling liquid is a silicone rubber which can have detrimental effects on the health of the patient if leaked into the blood stream. In whole, this is a complex design which is highly susceptible to thrombi emboli and improper function over time.
The Andersen valve comprises a stainless steel stent to secure a biological valve. The stent is formed of two or more wavy rings sutured to each other with the top loop requiring projecting apices to secure the commissural points of the valve. The valve claims reduced weight but looses this advantage by requiring multiple rings to attain patency against the tissue. The device requires a special trisection balloon with three or more projecting beads to secure the valve within the deployment catheter during placement, and the stent does not exert sufficient force against the tissue to remain in place without a balloon expanding the stent tightly into the tissue wall. The stiffness of stainless steel does not comply with the natural movement of the cardiovascular system which may lead to stenosis at the implantation point. Furthermore, the suture points connecting the multiple rings are subject to movement and wear against each other and therefore the sutures or the rings may break at the connecting points.
One drawback of all three of these valves is that none of the devices may be removed or repositioned once they are expressed from their placement catheter. Any misplacement or failure requires major open heart surgery equal to or greater than that now required by standard procedures. Many patients which receive the valve percutaneously because of their intolerance to surgery would face a very uncertain outcome from misplacement or failure. Also, none of these devices seal to the living tissue at the outside wall of the prosthesis. Leaks, and therefore emboli, are likely results after implantation.
The need remains for an artificial heart valve which is placed percutaneously through a single minimally invasive entry point; which will seal at the outside wall of the valve with the living tissue of the patient; which may be placed percutaneously at any point as well as directly over an existing vascular or cardiac valve; which will not cause thrombi emboli to form at the valve thereby removing the need for anticoagulant drugs; which will comply with the natural motion of the tissue to which it is attached; which will not cause stenosis; which does not require general anesthesia or stopping the heart or using a heart-lung machine during placement; which will reduce the recuperation time after placement both in and out of the hospital; and which may be repositioned or removed after placement in the event of such a need.